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Carbon seatpost catastrophe

Old 02-07-23, 10:27 AM
  #76  
Eric F
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Originally Posted by drlogik View Post
I will probably get blistered for this but this is my opinion...

A carbon seat post makes no sense to me. Carbon is EXTREMELY strong, as long as it is not compromised. A crack, a scratch, a crushed area OR over-stressing in my opinion can all compromise a carbon item (seat post, wheel, frame, fork, etc). That small circumference where it comes out of the seat tube is a vulnerable place. Over-tightening, a fall, or anything that stresses that one small area over time or repetitively can be a ticking catastrophe.

Carbon is great stuff but I would never put a carbon seat post on one of my bikes.
A scratch won't compromise CF unless it is deep enough to damage the integrity of the resin and fiber matrix. Following the installation specs for parts goes a very long way to the longevity of the parts, regardless of material. That said, some are more tolerant than others of hamfistedness.

I have some CF seatposts that are over 20 years old and still doing just fine.
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Old 02-07-23, 10:28 AM
  #77  
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Originally Posted by Eric F View Post
Your blame is still focused on the wrong thing.
A used carbon seatpost of unknown history, ridden for a time WAY past the minimum insertion by somebody who weighs about 270, and is over 6' tall, in a 47cm bike, then swapped to another bike and then not inserted enough, and possibly tightened down too much more than once because of slipping may be a bad choice for a large guy who rides rough.
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Old 02-07-23, 10:43 AM
  #78  
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It looks to me that this is a case of trying to save weight by buying a bike with a way too small of a frame. Then to make up for the small frame, a way too long of a seat post was used.
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Old 02-07-23, 10:58 AM
  #79  
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Originally Posted by LarrySellerz View Post
Today on the way home from work I felt something give in my saddle. I stopped to investigate, thinking it was coming loose, and to my horror I found that the seatpost was cracked and barely holding on! I still had 4 miles to go, and when I got home it was hanging on by a thread. It barely took any force to break it off (I got a video of myself kicking it off and it goes flying.)

it must have been a bit too high. it was previously installed way too high on another bike and could have been damaged then, or it could have been damaged in a crash I had last Friday. Hard to say. I donít have the metric Allen to pull it out and see how much is left in the frame.

a bike store told me previously that putting a long lever like I had could crack the aluminum frame. Would you be worried about the frame, or is it probably okay if it looks undamaged?

A bike shop told me a horror story of someone getting seriously injured by a broken seatpost. Do any of you have any horror stories?





Thanks again, Larry, you are indeed an artist at what you do.

For the usual crew who jump onto this excellent thread with the Carbon will be the death of anyone who uses this devils concoction its a bit late now. Carbon has been taking over the sport for the past 20 years or more, and your sky is falling narrative is losing its effect. The "steel is real" crew is like a doomsday cult which keeps missing its end-of-the-world date and preaching just wait, it's coming any day now.
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Old 02-07-23, 11:08 AM
  #80  
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Originally Posted by LarrySellerz View Post
Thats not very far above the minimum line...and its not his fault, hes a great mechanic. I was pushing the envelope though
He incorrectly installed a component but its not his fault?
um...
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Old 02-07-23, 11:12 AM
  #81  
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Originally Posted by georges1 View Post
That is why I never had a carbon seat post in any of my bikes.I never had trust in carbon seat posts,a guy who was doing a triathlon ona look kg171had his Look seat post fail after three years of intensive use. I prefer aluminium seat posts for many reasons.
Of course you do since you are staunchly analog.
I too am staunchly analog, but I recognize its simply preference rather than a dogmatic belief that it is somehow actually better in any instance I can opine on.

I have a carbon seatpost on my gravel bike. I am tall, its a sloping top tube, and there is a ton of seatpost showing. That thing is comfortable as a result. I have absolutely 0 fear of it breaking, relative to the old Easton aluminum seatpost it replaced. If either broke, I would consider it a freak incident instead of using it as a way to further solidify my bias.

Your example of some tri guy is of 0 use here. As a counter I could pull up countless examples of steel frames failing, but that doesnt mean stell is inherently weak, so I wont do something lazy like that.
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Old 02-07-23, 11:13 AM
  #82  
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Originally Posted by drlogik View Post
A carbon seat post makes no sense to me. Carbon is EXTREMELY strong, as long as it is not compromised. A crack, a scratch, a crushed area OR over-stressing in my opinion can all compromise a carbon item (seat post, wheel, frame, fork, etc). That small circumference where it comes out of the seat tube is a vulnerable place. Over-tightening, a fall, or anything that stresses that one small area over time or repetitively can be a ticking catastrophe.
One could cite a laundry list of reasons why an aluminum post makes no sense. Stress corrosion cracking, no fatigue limit, weak material, galvanic corrosion, etc.
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Old 02-07-23, 11:43 AM
  #83  
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Originally Posted by genejockey View Post
A used carbon seatpost of unknown history, ridden for a time WAY past the minimum insertion by somebody who weighs about 270, and is over 6' tall, in a 47cm bike, then swapped to another bike and then not inserted enough, and possibly tightened down too much more than once because of slipping may be a bad choice for a large guy who rides rough.
you tend to be good at following my stories. This is almost right except that this seatpost wasnít slipping. The only clue I have that it was overtightened is that it failed.

My point about the slipping seatpost was suggesting that having a seatpost where overtightening a commonly tightened bolt has a good chance of causing catastrophic failure is a design flaw.
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Old 02-07-23, 11:54 AM
  #84  
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Originally Posted by LarrySellerz View Post
you tend to be good at following my stories. This is almost right except that this seatpost wasnít slipping. The only clue I have that it was overtightened is that it failed.

My point about the slipping seatpost was suggesting that having a seatpost where overtightening a commonly tightened bolt has a good chance of causing catastrophic failure is a design flaw.
There are quite a few commonly tightened bolts on a bicycle where overtightening can cause catastrophic failure. Without carbon being present.
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Old 02-07-23, 12:16 PM
  #85  
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So far so good but I will stand by my opinion. Yes, other materials can fail also for the reasons I (and others) stated above. They include aluminum, steel and I'm sure titanium as well. And before you call me a carbon basher, I have the utmost confidence in carbon if it is applied in the appropriate manner.

I personally would not put a carbon seat post on my bike. I also would not put a relatively thin-walled aluminum seat post on my bike either. I have personally seen those fail. I'll take a few more pounds off my middle before I try to save a few ounces on my bike.

Many years ago we saw a snapped steel seat post come in on a kids bike. Don't ask me how.... The kid was ok and the dad wasn't walking funny. They said it just "broke". Heck, I managed to strip the crank on the bottom bracket spindle on a Raleigh Super Course back in the day so freak fails do occur.

Carbon has its permanent place in the cycling world, no doubt. I just don't trust it holding my bum up above a potential anal projectile.
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Old 02-07-23, 12:29 PM
  #86  
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Originally Posted by LarrySellerz View Post
My point about the slipping seatpost was suggesting that having a seatpost where overtightening a commonly tightened bolt has a good chance of causing catastrophic failure is a design flaw.
Not really. Lightweight carbon seatposts are made because there is a demand for them in the market. However, achieving that light weight means that they less resistant to things like over-torqueing of the binder bolt, and random lateral impact forces. It's not a design flaw, it's the side-effect of achieving the design goal. As such, the manufacturers have specific guidelines on how the seatpost is to be installed so as not to damage the structure. If you ignore those guidelines, you have exceeded the design parameters, and failure becomes an increasingly likely result. I own a torque wrench because operating within the manufacturer's safety guidelines matters to my health. Generally speaking, seatposts - like many other things - have 3 factors: 1) Light weight, 2) Low cost, 3) Durability. Pick 2.
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Old 02-07-23, 12:53 PM
  #87  
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Originally Posted by LarrySellerz View Post
My point about the slipping seatpost was suggesting that having a seatpost where overtightening a commonly tightened bolt has a good chance of causing catastrophic failure is a design flaw.
If the bolt was tightened properly, then the seat post wouldn't slip.
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Old 02-07-23, 01:00 PM
  #88  
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Originally Posted by LarrySellerz View Post
My point about the slipping seatpost was suggesting that having a seatpost where overtightening a commonly tightened bolt has a good chance of causing catastrophic failure is a design flaw.
WRONG.

Putting a part which has specific limits on a bike sold to someone who cannot understand basic thoughts is a problem ....

Mr. LarrySellerz, I am not trying to tear you up or knock you down, but Please, grow up.

If YOU overtighten a bolt out of Ignorance, don't blame the bolt. Blame the dolt.

Again .... like others here .... I am extremely overweight and have long exposed carbon-fiber seat posts and none of them have ever broken. The two times I have broken CF seat posts were both instances where I knew i was not inserting the post quite enough .... about as much too much as you had exposed. Other than that---see, some folks learn lessons from their mistakes-----I have never had a CF seat post break. The seat post broke because you used it incorrectly.

It is the same situation with your derailleur. If you kick it enough you will bend it and it will never work until you remove it and get everything back in line (don't ask how I know.) You cannot blame the derailleur designer or manufacturer. You deliberately misused and abused the part and damaged it. If you try to hammer a nail with a champagne flute, the subsequent breakage is not due to the bad design or manufacturer of the glass goblet.

Look--you can buy a pistol and if you shoot yourself in the foot, you cannot say that the gun manufacturer didn't make the barrel twelve feet long so you couldn't aim at yourself ...... you are supposed to be a responsible adult taking full responsibility for Your actions.

You are saying that if you tried to cut someone's hair with a chainsaw and cut off somebody's head, you don't blame the chainsaw manufacturer.

YOU messed up. You didn't bother to learn how to use what you bought, and you used it WRONG, and it broke----because YOU BROKE IT.
********************************************
That is really the crux of the issue: Stop Blaming People. Just be honest that you didn't learn how to use the part you bought and broke it. Take Responsibility. That way you will not make similar mistakes down the road.

Really, this isn't that big a deal. You abused a part, it broke, no big deal. I am sure a lot of us have made this error. I know I have, many times. No big deal.

The Big Deal portion of all this is that you step up and accept the consequences of your actions so that you can Not be in this same situation again later.

You can make the bike you showed---the Trek---work for you. Just do it right---a longer CF post, properly tightened, or an Al post.

On the other hand, you could completely mess up the new bike you showed us if you continue to misuse and abuse its component parts.

Your life, your choices.

Last edited by Maelochs; 02-07-23 at 01:04 PM.
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Old 02-07-23, 02:59 PM
  #89  
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CF seatpost are a bad idea. Iíve tightened dozens of seatposts and never once worried about potentially maiming someone if itís too tight. There is a time and place for carbon, and as demonstrated by this thread there is good arguments to be made for NOT having it in the seatpost.
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Old 02-07-23, 03:00 PM
  #90  
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Originally Posted by elcruxio View Post
There are quite a few commonly tightened bolts on a bicycle where overtightening can cause catastrophic failure. Without carbon being present.
name 2, and they should be easily overtightened
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Old 02-07-23, 03:14 PM
  #91  
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Originally Posted by LarrySellerz View Post
CF seatpost are a bad idea. Iíve tightened dozens of seatposts and never once worried about potentially maiming someone if itís too tight. There is a time and place for carbon, and as demonstrated by this thread there is good arguments to be made for NOT having it in the seatpost.
I would agree that CF seatposts are a bad idea FOR YOU. For many other people who follow correct installation protocols, they are not an issue. You've talked about the seatpost bolt being frequently used. Again, maybe that's the case FOR YOU, and another reason why CF is a bad material option FOR YOU. Personally, I have bikes where the seatpost bolt hasn't been touched in years. On my newest bike, I've turned stem and handlebar bolts a LOT more than the seatpost bolt in the past couple of months while trying to fine-tune my fit. Making a blanket claim that CF is a bad choice for seatposts, in all situations, for every user, is just false.
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Old 02-07-23, 03:16 PM
  #92  
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Originally Posted by LarrySellerz View Post
Iíve tightened dozens of seatposts and never once worried about potentially maiming someone if itís too tight.
Why are you worried? You don't own a metric Allen wrench, so there's no chance you could ever over tighten a carbon seat post.
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Old 02-07-23, 03:16 PM
  #93  
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Originally Posted by LarrySellerz View Post
name 2, and they should be easily overtightened
Steerer tube bolts. Handlebar bolts. They generally have the same/similar torque specs as seatposts. Overtightening has the same potential issues as a seatpost - eventual failure.
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Old 02-07-23, 03:27 PM
  #94  
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Originally Posted by LarrySellerz View Post
CF seatpost are a bad idea. Iíve tightened dozens of seatposts and never once worried about potentially maiming someone if itís too tight. There is a time and place for carbon, and as demonstrated by this thread there is good arguments to be made for NOT having it in the seatpost.
No. This thread does not contain any "good arguments" against the use of carbon fibre seat posts. None. A good argument advances good reasons, supported by relevant evidence. Both elements are absent here.

All that this thread has demonstrated, to this point, is that using a carbon fibre seat post might be a bad idea for you, and possibly for any third-parties who have installed a carbon fibre seat post for you. There is some evidence here to support those two claims.
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Old 02-07-23, 04:12 PM
  #95  
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Originally Posted by badger1 View Post
No. This thread does not contain any "good arguments" against the use of carbon fibre seat posts. None.
Every single broken carbon seatpost anecdote is a perfectly fine argument against their use, all by itself. Especially so when compared to the relative lack of broken non-carbon seatpost anecdotes.
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Old 02-07-23, 04:26 PM
  #96  
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Originally Posted by Fredo76 View Post
Every single broken carbon seatpost anecdote is a perfectly fine argument against their use, all by itself. Especially so when compared to the relative lack of broken non-carbon seatpost anecdotes.
Ahem.

Originally Posted by terrymorse View Post
Aluminum posts also break. I was riding behind a ride buddy when he went over a bump, and the post snapped right off, leaving a just a sharp point sticking out. We rode for another hour like that, and I rode out of the saddle as an act of support.
Originally Posted by GhostRider62 View Post
When your aluminum SP breaks and when you come to, the ambulance is there to take you to the ER. That is the real thing and not fun, trust me.
Originally Posted by skidder View Post
I had an aluminum post break a while back. IT broke in the cast headpiece area that connects to the rails on the underside of the saddle. I felt it getting 'slushy' (?), got off, and noticed the crack. Lucky for me I was only about 2 miles/3Km from home so just rolled back. Now I just tighten the saddle adjustment until it doesn't move, then maybe a 1/4 turn more and I'm good.
Originally Posted by big john View Post
I was riding up Mulholland Hwy following a friend when his American Classic post failed and he fell on a massive hematoma which he obtained a week earlier when a dog took him down. He put the saddle in his pocket and finished the climb. I did not stand in solidarity.

Of course, I had one (American Classic) fail when I was solo above Lake Casitas. Luckily I did not fall.
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Old 02-07-23, 04:28 PM
  #97  
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Originally Posted by Fredo76 View Post
Every single broken carbon seatpost anecdote is a perfectly fine argument against their use, all by itself. Especially so when compared to the relative lack of broken non-carbon seatpost anecdotes.
This thread includes anecdotal evidence of broken non-carbon seatposts as well. One could conclude that neither CF, nor aluminum, are good materials for seatposts.
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Old 02-07-23, 04:34 PM
  #98  
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Originally Posted by terrymorse View Post
One could cite a laundry list of reasons why an aluminum post makes no sense. Stress corrosion cracking, no fatigue limit, weak material, galvanic corrosion, etc.
I have aluminum seat posts on all 3 of my bikes and never experienced any of the problems you just mentioned.
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Old 02-07-23, 04:35 PM
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Originally Posted by genejockey View Post
Ahem.
Those are all good arguments against extra-light aluminum seatposts, I assume.

I want a seatpost that won't break. They didn't used to break, iirc.

Luckily, all of mine qualify.
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Old 02-07-23, 04:39 PM
  #100  
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Originally Posted by wolfchild View Post
I have aluminum seat posts on all 3 of my bikes and never experienced any of the problems you just mentioned.
This doesn't mean that it's not a possibility for other people. In exactly the same way, I have 6 CF seatposts on my current bikes that have never had problems, including some that are 20+ years old. Yet, despite my success, other people have had failures, for various reasons.
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